Clicking on button "A" below should yield an address ending in "?button_a=value_a" and nothing more. Clicking on button "B" below should yield an address ending in "?button_b=value_b" and nothing more.
If your browser doesn't implement the HTML 4 specification correctly, nothing happens when you click. (The default type "submit" is not applied).
Clicking on button "X" below should yield an address ending in "?button_x=value_x" and nothing more. Clicking on button "Y" below should yield an address ending in "?button_y=value_y" and nothing more.
If your browser doesn't implement the HTML 4.0 specification correctly, the address will end in "?button_x=X&button_y=Y" regardless of which button you pressed (the button-elements are not treated as input-elements would be).